Effluent Gas Scrubbing

ABSTRACT

An effluent gas scrubber and a method of scrubbing effluent gases are provided. An inlet port receives an effluent gas. The gas passes through successive chambers in which it is sprayed with a scrubbing fluid. An oxidizer within the scrubbing fluid is effective to oxidize non-water soluble gases within the effluent gas. An oxidation-reduction potential probe measures the oxidation-reduction potential of the scrubbing fluid and adds the oxidizer to the scrubbing fluid as needed. A pH probe measures the pH of the scrubbing fluid and adds a base to the scrubbing fluid as needed to maintain the pH at or above a threshold such as pH 7, or pH 12.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of and claims the benefit of U.S.patent application Ser. No. 11/891,075, now U.S. Pat. No. ______, filedAug. 8, 2007 and titled “Effluent Gas Scrubber and Method of ScrubbingEffluent Gasses,” which claims the benefit of U.S. Provisional PatentApplication No. 60/836,905 filed on Aug. 9, 2006 and titled “Apparatusand Method for Oxidizing Pollutants in Effluent Gas Streams,” each ofwhich is incorporated herein by reference. This application is generallyrelated to U.S. Pat. No. 4,986,838 titled “Inlet System for GasScrubber,” issued to Johnsgard on Jan. 22, 1991, and also incorporatedherein by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to scrubbing of effluent gases and moreparticularly to scrubbing of gases that are not water soluble.

2. Description of the Prior Art

Various gases, some toxic and some highly corrosive or reactive, areused in semiconductor manufacturing processes. Scrubbers are used forcleansing any mixture of gases that remains at the conclusion of amanufacturing procedure. Most such scrubbers operate by passing themixture of gases through a mist of a fluid such as water; thesescrubbers are known as wet fume scrubbers. Some gases, of which a fewexamples are chlorine, fluorine and ammonia, are water soluble and arereadily removed by this method. Other gases such as silane (SiH₄),arsine (AsH₃), phosphine (PH₃), and germane (GeH₄) are not watersoluble. A shortcoming of wet fume scrubbers has been their inability toremove gases such as silane that are not water soluble.

Many water-insoluble gases are oxidizable and in principle can bedisposed of with the assistance of an oxidizing agent such as oxygen.Various systems and methods based on the use of an oxidizing agent toremove water-insoluble gases have been proposed. Among these are U.S.Pat. No. 5,271,908 issued to Shiban et al. on Dec. 21, 1993, U.S. Pat.No. 6,084,148 issued to Shiban et al. on Jul. 4, 2000, U.S. patentapplication Ser. No. 09/957,424 filed Sep. 21, 2001 by Tong et al. andpublished Mar. 27, 2003 as Publication No. 2003/0057576, U.S. patentapplication Ser. No. 10/849,435 filed May 19, 2004 by Arno et al. andpublished Oct. 28, 2004 as Publication No. 2004/0213721, U.S. patentapplication Ser. No. 11/217,780 filed Sep. 1, 2005 by Tong et al. andpublished Jan. 5, 2006 as Publication No. 2005/0002380.

A 1998 German report bearing the identifier Forderkennzeichen 254 116 98and titled “Verfahrensentwicklung zur Herstellung von Solar-Silicium imhalbtechnischen” also addresses the problem. This last reference reportson a laboratory test of a benchtop replication of a scrubber. The testreported on the reaction of silane with sodium hydroxide or potassiumhydroxide. Sodium hypochlorite was also added as an oxidation agent butshowed no influence on the silane conversion. The report noted thatsmall flames were observed in those experiments that employed sodiumhypochlorite due to gas bubbles on the liquid surface. The reportconcluded, with respect to the use of sodium hypochlorite that addingsodium hypochlorite is dangerous because of the intense reaction withsilane. Accordingly, there remains a need for a safe and economical wayto scrub gases that are not water soluble from an effluent gas mixture.

SUMMARY

Briefly and in general terms, an effluent gas scrubber according to theinvention has an inlet port for receiving an effluent gas, a firstchamber that receives the gas from the inlet port, a second chamber thatreceives the gas from the first chamber, and an outlet port. Eachchamber has a nozzle oriented to spray a scrubbing fluid. Anoxidation-reduction potential (ORP) probe measures theoxidation-reduction potential of the scrubbing fluid and adds anoxidizer as needed to the scrubbing fluid. Likewise, a pH probe measuresthe pH of the scrubbing fluid and adds an acid or base to the scrubbingfluid as needed to maintain the pH at above or below a desired level.The desired level may be pH 7 or in some cases as much as pH 12 orhigher. In some embodiments, an interior surface of a transition tubebetween the inlet port and the first chamber may be coated with aswirling fluid.

A method of scrubbing an effluent gas according to the inventionincludes adding an oxidizer to a reservoir of scrubbing fluid, sprayingthe scrubbing fluid through an effluent gas, measuring theoxidation-reduction potential and/or the pH of the scrubbing fluid, andadding oxidizer and/or a base to the scrubbing fluid. The oxidizer iseffective to oxidize non-water soluble gases from the effluent gas thatwould not otherwise be removed by the scrubbing fluid. The baseincreases the pH of the washing solution, preferably to pH 7 or above,in some embodiments.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic of a scrubber according to an exemplary embodimentof the invention.

FIG. 2 is a cross-sectional view of a gas inlet port of the embodimentof FIG. 1.

FIG. 3 is a flowchart of a method according to an exemplary embodimentof the invention.

DETAILED DESCRIPTION OF THE INVENTION

There has been a need for a way to remove gases that are not watersoluble from a flow of effluent gases. In an effluent gas scrubberembodying the invention, an effluent gas passes through successivechambers within which it is sprayed with a scrubbing fluid. An ORP probemeasures the oxidation-reduction potential of the scrubbing fluid tocontrol the addition of an oxidizer to the scrubbing fluid as needed tomaintain the oxidizer concentration, so as to oxidize and thereby removenon-soluble gases such as silane. A pH probe can also be used to measurethe pH of the scrubbing fluid to control the addition of a base to thescrubbing fluid to compensate for the acidification of the scrubbingfluid by the uptake of the various water-soluble gases. In someembodiments, an interior surface of a passage between the inlet port andthe first chamber may be coated with a swirling fluid to reduceclogging. The swirling fluid prevents the nucleation and growth ofcondensation on the interior surface, and also produces little mist orvapor to support cooling and condensation.

Referring to FIG. 1, an effluent gas scrubber embodying the principlesof the invention has an inlet port 101 that receives an effluent gasmixture for scrubbing. A scrubbing fluid reservoir 103 stores ascrubbing fluid 105. Water or some other suitable substance may be usedas the scrubbing fluid. A first chamber 107 is in fluid communicationwith the inlet port 101 through an opening 109, and a nozzle 111 isoriented to spray fluid 105 from the scrubbing fluid reservoir 103 intothe first chamber 107. A second chamber 113 is in fluid communicationwith the first chamber 107 through an opening 115, and a nozzle (shownas a plurality of individual nozzles 117, 119, 121 and 123) in thesecond chamber 113, in fluid communication with the scrubbing fluidreservoir 103, is oriented to spray fluid 105 from the scrubbing fluidreservoir 103 into the second chamber 113. An outlet port 125 is influid communication with the second chamber 113. Another embodiment mayuse only a packed bed and no spray chambers.

An oxidizer tank 127 stores an oxidizer 129. Exemplary oxidizers includehydrogen peroxide, potassium permanganate, sodium hypochlorite, oxygen,and ozone. As used herein, hydroxides such as sodium and potassiumhydroxides, are expressly not oxidizers 129 but are instead bases. AnORP probe 131 measures the oxidation-reduction potential of thescrubbing fluid 105 in the scrubbing fluid reservoir 103 and, responsiveto the measured potential, causes the oxidizer 129 to flow from theoxidizer tank 127 to the scrubbing fluid reservoir 103.

An oxidizer pump 133 may be used to pump oxidizer 129 from the oxidizertank 127 to the scrubbing fluid reservoir 103 according to the potentialmeasured by the ORP probe 131. For example, an oxidizer controller 135,responsive to the ORP probe 131, may be used to control the oxidizerpump 133. The oxidizer 129 flows through a suitable passage 137 from theoxidizer tank 127 to the oxidizer pump 133 and then to the scrubbingfluid reservoir 103 through a passage 139. The ORP controller 135 isconnected to the ORP probe 131 through a lead 141 and to the oxidizerpump 133 through a lead 143. Instead of controlling the delivery of theoxidizer 129 by measuring the oxidation-reduction potential of thescrubbing fluid 105, the oxidizer 129 can optionally be added to thescrubbing fluid reservoir 103 at a preset rate that depends upon thetype and flow rate of the gas to be oxidized. The oxidizer pump 133 canalso be slaved to a gas flow controller and operated at a rateproportional to the effluent gas flow.

In a similar manner, a pH probe 171 measures the pH potential of thescrubbing fluid 105 in the scrubbing fluid reservoir 103 and, responsiveto the measured pH, causes a base 173 to flow from a base tank 175 tothe scrubbing fluid reservoir 103. A base pump 177 may be used to pumpbase 173 from the base tank 175 to the scrubbing fluid reservoir 103according to the pH measured by pH probe 171. For example, a pHcontroller 181, responsive to the pH probe 171, may be used to controlthe base pump 177. The base 173 flows through a suitable passage 183from the base tank 175 to the base pump 177 and then to the scrubbingfluid reservoir 103 through a passage 185. The pH controller 181 isconnected to the pH probe 171 through a lead 187 and to the base pump177 through a lead 189.

The pH controller 181 may engage the base pump 177 whenever it sensesthat the pH of the scrubbing fluid 105 has fallen below a predefinedthreshold. This can happen, for example, if the scrubbing fluid 105becomes acidic as a result of water-soluble gases that enter the fluid105 during the scrubbing process. In one embodiment it may be sufficientto maintain the pH at or above a level of pH 7. In another embodiment,for example, if the gases being scrubbed are very acidic, it may bedesirable to maintain a pH of pH 12 or more. The pH control may beenhanced, in some instances, by means of a pre-scrubber chamber (notshown) with a separate scrubbing fluid to remove any strongly acidic gassuch as HCl or chlorosilane. Generally, the pH of the scrubbing fluid105 needs to be at pH 7 or above as a pH below pH 7 will prevent someoxidizers from being effective. Instead of controlling the delivery ofthe base 173 by measuring the pH of the scrubbing fluid 105, the base173 can optionally be added to the scrubbing fluid reservoir 103 at apreset rate that depends upon the type and flow rate of thewater-soluble gases to be scrubbed. The base pump 177 can likewise beslaved to the gas flow controller and operated at a rate proportional tothe effluent gas flow.

Any suitable pumping device may be used as the oxidizer pump 133 or thebase pump 177. Alternatively, the oxidizer 129 and base 173 may flowinto the scrubbing fluid reservoir 103 by gravity, in which case anysuitable valve can be used to control the flow of the oxidizer 129 orthe base 173.

Location of the ORP probe 131 in the scrubbing reservoir 103, andselection of a point 165 at which the oxidizer 129 is injected into thescrubbing fluid reservoir 103, may be done such that the oxidizer 129enters a pump 157 quickly for rapid dispersal through the scrubbingfluid 105 and the ORP probe 131 is exposed to the oxidizer 129 as soonas possible after injection. For example, the injection point 165 can belocated near an inlet to the pump 157 and the ORP probe 131 located nearan outlet of the pump 157. This allows for good mixing and fast feedbackto the controller 135 for tighter control. Accurate metering of theoxidizer 129 allows the minimum effective concentration to bemaintained, reducing the chance of a violent oxidizing reaction,especially with silane or germane gases. These same principles apply tothe location of an injection point 186, at which base 173 can beinjected into scrubbing fluid reservoir 103, and the location of pHprobe 171, suitable for measuring the pH of scrubbing fluid 105.

Some embodiments employ a packed column 145. Gases can flow into thecolumn 145 from the second chamber 113, for example through a passage147. The column 145 can be filled with plastic spherical frames, forexample, that offer a substantial area of wetted surface. The gases flowinto the column 145 through an eductor 149. In the embodiment shown, theeductor 149 includes a high-flow, full-cone, narrow-spray nozzle 151 anda cone 153. The flow of scrubbing fluid 105 through the nozzle 151 andthe cone 153 carries the effluent gases along with it and thereby lowersupstream gas pressure.

The nozzle 151 may receive scrubbing fluid 105 from the scrubbing fluidreservoir 103 through plumbing 155 connected to pump 157. The pump 157may also provide scrubbing fluid to the other nozzles 111, 117, 119, 121and 123. Preferably the pump 157 is constructed of corrosion-resistantmaterials for protection from corrosives that may build up in thescrubbing fluid 105.

Precipitate build up in the packed column 145 is avoided in two ways.First, by the time the effluent gases reach the packed column 145, mostof the reactive gases have already been removed. Second, the nozzle 151above the packed column supplies a sufficiently large flow of scrubbingfluid 105 to prevent solids from building up in the column 145.

After the effluent gases pass through the packed column 145, a finalnozzle 159 sprays the gases as they enter the outlet port 125. Freshwater may be used for this final spray. The final nozzle 159 mayinclude, in some embodiments, a plurality of full cone, fine spraynozzles. This fresh water spray gives the scrubbed gases one more washof maximum absorption fresh water to ensure the highest possiblescrubbing efficiency before the gases exit to the atmosphere. It alsoencircles the entrance to the exhaust outlet port 125 and prevents anyfoam that may have formed on the surface of the scrubbing fluid 105 inthe scrubbing fluid reservoir 103 from exiting through the outlet port125.

In one embodiment the nozzle 111 in the first chamber 107 may be ahigh-flow, large-droplet, full-cone-spray nozzle. A spray 161 ofscrubbing fluid 105 from this nozzle 111, in addition to providing thefirst scrub of the effluent gases, keeps surfaces in the first chamber107 flushed so as to prevent coating or deposits. The nozzles 117, 119,121 and 123 may be low-flow, small-droplet nozzles that provide a spray163 having a large surface area and traveling faster than the effluentgases, resulting in efficient scrubbing. In other embodiments, differentkinds of nozzles may be used according to such factors as the types ofgases being scrubbed and the physical configuration of the scrubber.

As shown in FIG. 2, a transition tube 201 may be provided between theinlet port 101 and the first chamber 107. An input reservoir 203surrounds an inlet pipe 205 adjoining the transition tube 201. Aswirling fluid from the reservoir 203 is introduced into the transitiontube 201 through an opening 207 such that interior surfaces of thetransition tube 201 are coated with the swirling fluid.

In the embodiment shown in FIG. 2, a plurality of jets 209 and 211 aredisposed in the reservoir 203 and receive fluid from a pump (not shown)through a fluid inlet 213 and an annular conduit 215. The fluid swirlsaround the reservoir and thence into the transition tube 201 through theopening 207. Other means than the jets might be used to swirl the fluid.For example, an impeller blade in the reservoir, activated for exampleby a drive shaft or a magnetic field, could make the fluid swirl. Or thefluid could be made to swirl by vibrating the reservoir 203 or byrotating the reservoir 203 or (if the fluid is electrically conductive)by a rotating magnetic field. In the embodiment shown, the reservoir 203is coupled to a supply pipe 217 in which the inlet port 101 is locatedby a union 219 and a nut 221.

A plunger 223 may be held in a retainer 225 coupled to the supply pipe217 by a nut 227, in some embodiments. The plunger 223 is disposed in aposition from which it may be extended through the inlet pipe 205 asnecessary for cleaning. The plunger 223 may be actuated manually by anactuator 229 or by electric or mechanical means (not shown) based on avisual inspection, a time interval, a backpressure measurement, or thelike. A scraper, a file, or some other appropriate tool can also be usedin place of the plunger 223 to remove deposits from the inlet pipe 205.Further details and alternative embodiments of the inlet port 101 andtransition tube 201 are described in U.S. patent application Ser. No.10/804,764 filed on Mar. 14, 2004 and titled “Apparatus and Method forProviding Heated Effluent Gases to a Scrubber,” which is incorporatedherein by reference.

An embodiment of a method of scrubbing an effluent gas according to theprinciples of the invention is illustrated in FIG. 3. The method beginsby adding an oxidizer to a reservoir of scrubbing fluid (301). Thescrubbing fluid is then sprayed through an effluent gas (303). Non-watersoluble gases such as silane are readily oxidized by the oxidizer, whilewater soluble gases are removed by the scrubbing fluid. Theoxidation-reduction potential of the scrubbing fluid is measured (305)and a sufficient quantity of oxidizer is added to the scrubbing fluid tomaintain the oxidation-reduction potential (307). The pH of thescrubbing fluid may also be measured so that a sufficient quantity ofbase can be added to the scrubbing fluid to maintain the pH above apredefined threshold. In one embodiment the predefined pH threshold isabout 7, and in another the predefined pH threshold is about 12. Otherlevels may be defined as desired. In some embodiments, the effluent gasis sprayed with fresh water after having been sprayed with the scrubbingfluid (309).

In the foregoing specification, the invention is described withreference to specific embodiments thereof, but those skilled in the artwill recognize that the invention is not limited thereto. Variousfeatures and aspects of the above-described invention may be usedindividually or jointly. Further, the invention can be utilized in anynumber of environments and applications beyond those described hereinwithout departing from the broader spirit and scope of thespecification. The specification and drawings are, accordingly, to beregarded as illustrative rather than restrictive. It will be recognizedthat the terms “comprising,” “including,” and “having,” as used herein,are specifically intended to be read as open-ended terms of art.

1. An effluent gas scrubber comprising: an inlet port; a scrubbing fluidreservoir; a first chamber in fluid communication with the inlet port; anozzle in the first chamber, in fluid communication with the scrubbingfluid reservoir and oriented to spray fluid from the scrubbing fluidreservoir into the first chamber; a second chamber in fluidcommunication with the first chamber; a nozzle in the second chamber, influid communication with the scrubbing fluid reservoir and oriented tospray fluid from the scrubbing fluid reservoir into the second chamber;a pH probe that measures the pH of a fluid in the scrubbing fluidreservoir and responsive to the measured pH causes an addition of anacid or a base to the fluid; an outlet port in fluid communication withthe second chamber; an oxidizer tank; and an oxidation-reductionpotential probe that measures the oxidation-reduction potential of fluidin the scrubbing fluid reservoir and responsive to the measuredoxidation-reduction potential adds an oxidizer to the fluid.
 2. Theeffluent gas scrubber as in claim 1 further comprising an oxidizer pumpunder control of the oxidation-reduction potential probe that addsoxidizer to the fluid.
 3. The effluent gas scrubber as in claim 1wherein the pH probe causes an addition of base if the pH is less than7.
 4. The effluent gas scrubber as in claim 1 wherein the pH probecauses an addition of base if the pH is less than
 12. 5. The effluentgas scrubber as in claim 1 further comprising: a packed column defininga fluid path between the second chamber and the outlet port; and aneductor in the fluid path and in fluid communication with the scrubbingfluid reservoir and oriented to spray effluent gas from the secondchamber and fluid from the scrubbing fluid reservoir into the packedcolumn.
 6. The effluent gas scrubber as in claim 1 further comprising: atransition tube between the inlet port and the first chamber; an inputreservoir adjacent the transition tube; and means for introducing aswirling fluid from the reservoir into the transition tube such that aninterior surface of the transition tube is coated with the swirlingfluid.
 7. The effluent gas scrubber as in claim 6 further comprising: aninlet pipe between the inlet port and the transition tube; and a plungerconfigured to be extendable through the inlet pipe to remove a depositon an inner surface on any of the inlet pipe and transition tube.
 8. Ascrubber for scrubbing an effluent gas using a scrubbing fluid, thescrubber comprising: a first chamber; an inlet port configured todeliver the effluent gas to the first chamber; a scrubbing fluidreservoir configured to deliver the scrubbing fluid to the firstchamber; a pH probe configured to measure the pH of the scrubbing fluid;and a tank configured to add an acid or a base to the scrubbing fluid inresponse to the measured pH.
 9. The scrubber of claim 8, wherein thetank includes a base tank, and the base is added in response to ameasured pH below
 7. 10. The scrubber of claim 8, wherein the tankincludes a base tank, and the base is added to the scrubbing fluid inresponse to a measured pH below
 12. 11. The scrubber of claim 8, whereinthe addition of the acid or base is at a preset rate.
 12. The scrubberof claim 11, wherein the preset rate depends upon a flow rate of theeffluent gas.
 13. The scrubber of claim 8, further comprising anoxidation-reduction potential probe that measures theoxidation-reduction potential of the scrubbing fluid.
 14. The scrubberof claim 13, further comprising an oxidizer pump to deliver an oxidizerto the scrubbing fluid, the oxidizer pump controlled by theoxidation-reduction potential probe.
 15. The scrubber of claim 8,wherein the first chamber includes a packed bed.
 16. The scrubber ofclaim 8, wherein the first chamber includes a packed column.
 17. Thescrubber of claim 8, wherein the first chamber includes one or morenozzles configured to spray the scrubbing fluid into the first chamber.18. The scrubber of claim 8, wherein the base includes one or morehydroxides.
 19. The scrubber of claim 8, wherein the effluent gasincludes a first gas that lowers the pH of the scrubbing fluid upondissolution in the scrubbing fluid.
 20. The scrubber of claim 8, furthercomprising a second chamber in fluid communication with the firstchamber and configured to receive the effluent gas from the firstchamber.
 21. A method of scrubbing an effluent gas comprising: receivingthe effluent gas into a chamber; adding a scrubbing fluid to thechamber; and controlling a pH of the scrubbing fluid in response to theeffluent gas.
 22. The method of claim 21, wherein controlling includesadding an acid or a base to the scrubbing fluid.
 23. The method of claim22, wherein controlling includes measuring the pH of the scrubbingfluid, and the acid or base is added in response to the measured pH. 24.The method of claim 24, wherein controlling includes adding a base whenthe pH is below
 12. 25. The method of claim 21, further comprisingmeasuring an oxidation-reduction potential of the scrubbing fluid. 26.The method of claim 21, further comprising adding an oxidizer to thescrubbing fluid.